1. Field of the Invention
The present invention relates to an ultrasonic touch panel system for sensing a touch position on a nonpiezoelectric plate by means of using first- and second transducer-units, first- and second detecting-units, and a signal analyzer.
2. Description of the Prior Art
Conventional touch panels include, in general, a wedge-shaped transducer for vibrating a nonpiezoelectric plate indirectly, or a piezoelectric thin film transducer for vibrating a nonpiezoelectric plate directly. Such conventional touch panels detect an output electric signal, which disappears in response to a disappearance of an ultrasound on a nonpiezoelectric plate by touching thereon, and sense a touch position from a disappearance of the output electric signal. Thus, conventional touch panels cause a high voltage operation with a high power consumption, and a large-scale circuit with a complicated structure.
An object of the present invention is to provide an ultrasonic touch panel system capable of detecting first- and second delayed electric signals by touching a nonpiezoelectric plate with a high sensitivity and a quick response time.
Another object of the present invention is to provide an ultrasonic touch panel system excellent in manufacturing.
Another object of the present invention is to provide an ultrasonic touch panel system operating under low electric power consumption with low voltage.
A still other object of the present invention is to provide an ultrasonic touch panel system having a small-sized circuit with a simple structure which is very light in weight.
According to one aspect of the present invention there is provided an ultrasonic touch panel system comprising a nonpiezoelectric plate, first- and second transducer-units, first- and second detecting-units, and a signal analyzer connected to the first- and second detecting-units. The first transducer-unit consists of at least two input interdigital electrodes Txi (i=1, 2, . . . , m), at least two electrode groups Gxi (i=1, 2, . . . , m) corresponding with the input interdigital electrodes Txi, respectively, first- and second piezoelectric substrates, and at least two uniting terminals Uxj (i=1, 2, . . . , n). The input interdigital electrodes Txi and the electrode groups Gxi are formed on first- and second edges, respectively, of an upper end surface of the nonpiezoelectric plate. The first- and second piezoelectric substrates are cemented on the input interdigital electrodes Txi and the electrode groups Gxi, respectively. Two neighbors of the electrode groups Gxi consist of at least two output interdigital electrodes Rxaj (j=1, 2, . . . , n) and at least two output interdigital electrodes Rxbj (j=1, 2, . . . , n), respectively. The output interdigital electrodes Rxaj have the reverse electrode-finger directions from the output interdigital electrodes Rxbj. The uniting terminals Uxj are connected to the output interdigital electrodes Rxaj, respectively, and also to the output interdigital electrodes Rxbj, respectively. The second transducer-unit has the same construction as the first transducer-unit, and consists of at least two input interdigital electrodes Tyi (i=1, 2, . . . , m), at least two electrode groups Gyi (i=1, 2, . . . , m), third- and fourth piezoelectric substrates, and at least two uniting terminals Uyj (j=1, 2, . . . , n). The input interdigital electrodes Tyi and the electrode groups Gyi are formed on third- and fourth edges, respectively, of the upper end surface of the nonpiezoelectric plate. The third and fourth piezoelectric substrates are cemented on the input interdigital electrodes Tyi and the electrode groups Gyi, respectively. Two neighbors of the electrode groups Gyi consist of at least two output interdigital electrodes Ryaj (j=1, 2, . . . , n) and at least two output interdigital electrodes Rybj (j=1, 2, . . . , n), respectively. The output interdigital electrodes Ryaj have the reverse electrode-finger directions from the output interdigital electrodes Rybj. The uniting terminals Uyj are connected to the output interdigital electrodes Ryaj, respectively, and also to the output interdigital electrodes Rybj, respectively. The first detecting-unit consists of a fifth piezoelectric substrate, first-, second-, and third interdigital electrode pairs formed on the fifth piezoelectric substrate, and a first synchronizing device. The second detecting-unit has the same construction as the first detecting-unit, and consists of a sixth piezoelectric substrate, fourth-, fifth-, and sixth interdigital electrode pairs formed on the sixth piezoelectric substrate, and a second synchronizing device.
When a first input electric signal is applied to two neighbors of the input interdigital electrodes Txi simultaneously, a first surface acoustic wave (SAW) is excited in the first piezoelectric substrate, The first SAW is transmitted to the second piezoelectric substrate along the upper end surface of the nonpiezoelectric plate, and transduced to a first output electric signal at the output interdigital electrodes Rxaj and Rxbj, respectively. Thus, ixc3x97j first-SAW lanes in all are formed between the input interdigital electrodes Txi and the electrode groups Gxi. In the same way, ixc3x97j second-SAW lanes in all are formed between the input interdigital electrodes Tyi and the electrode groups Gyi.
If touching nowhere on the upper end surface of the nonpiezoelectric plate, no delayed electric signal appears at all the uniting terminals. However, if touching anywhere on the upper end surface of the nonpiezoelectric plate, a first delayed electric signal appears at one of the uniting terminals Uxj, and a second delayed electric signal appears at one of the uniting terminals Uyj. The first delayed electric signal arrives not only at the signal analyzer directly, but also at the signal analyzer indirectly via the first detecting-unit. As a result, the first delayed electric signal is converted into a first burst-signal. An amplitude condition of the first burst-signal indicates which of two neighbors of the electrode groups Gxi causes the first delayed electric signal appearing at one of the uniting terminals Uxj. In the same way, the second delayed electric signal is converted into a second burst-signal. An amplitude condition of the second burst-signal indicates which of two neighbors of the electrode groups Gyi causes the second delayed electric signal appearing at one of the uniting terminals Uyj. Thus, it is possible to sense the touch position by distinguishing a phase condition of the first delayed electric signal appearing at one of the uniting terminals Uxj and that of the second delayed electric signal appearing at one of the uniting terminals Uyj.
According to another aspect of the present invention there is provided a piezoelectric substrate with a window-flame shape in place of the first-, second-, third-, and fourth piezoelectric substrates.
According to another aspect of the present invention there are provided first-, second-, third-, fourth-, fifth-, and sixth piezoelectric substrates, made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a transparent nonpiezoelectric plate.
According to another aspect of the present invention there are provided first-, second-, third-, and fourth piezoelectric substrates having a thickness smaller than an interdigital periodicity of the input interdigital electrodes Txi and Tyi. In addition, there is provided a nonpiezoelectric plate having a thickness larger than three times the interdigital periodicity.
According to other aspect of the present invention there is provided an ultrasonic touch panel system, wherein the phase velocity of the surface acoustic wave on the nonpiezoelectric plate alone is higher than that in the first-, second-, third-, and fourth piezoelectric substrates alone.
According to a further aspect of the present invention there are provided a first switch connected with the input interdigital electrodes Txi, and a second switch connected with the input interdigital electrodes Tyi.